The objectives are two-fold: 1) to elucidate the role of conformational changes, segmental flexibility, and domain interactions in the molecular mechanism of effector activation in IgM and IgG, and 2) to study the tertiary structure of the combining site of a new murine IgM myeloma protein produced by ABPC 22 which binds fluorescent antigens. These problems will be investigated primarily by means of nanosecond fluorescence and circular dichroism techniques which are currently utilized in our laboratory and have been shown to be feasible. Our specific aims for the project period are to : 1) determine the role of the C mu 2 domains of Igm in the transfer of information from the antibody combining site in Fab to the complement activation site in Fc. 2) To determine the biological effects of segmental flexibility in IgG by measurement of any changes in flexibility caused by hapten binding at the active site. 3) To correlate spectroscopic properties of bound fluorescent lingad with specific interactions and structure of the site of ABPC 22. This will be done by measurement of fluorescence and induced CD of DNS and fluorescein bound to ABPC 22 and comparison with properties of naturally elicited antibodies to these fluorophores. Sequencing of the L and H chains, at least through the first hypervariable regions, will be done. Attempts will be made to crystallize the Fab and, if successful, collaboration with an appropriate laboratory for x-ray diffraction will be initiated.